Transparent heat-sealable sheets carrying vapor phase corrosion inhibitors



March 5, 1963 w. A. FEssLER ErAL 3,080,211

TRANSPARENT HEAT-SEALABLE SHEETS CARRYING VAPOR PHASE coRRosIoN INHIBIToRs Filed May 15, 1959 United States Patent 3,080,211 TRANSPARENT HEAT-SEALABLE SHEETS CARRY ING VAPQR PHASE CORROSION INHIBITORS William Alfred Fessler, Hopeweil, Va., and Clemens A. Hutter, Eimhurst, Harry L. Buckmaster, Harvey, and George 0. Stricker, Bine Island, Ill., assignors to Danbert Chemical Company, Chicago, lll., a corporation of Illinois Filed May 1S, 1959, Ser. No. 813,440 12. Claims. (Cl. 2l-2.5)

This invention relates to vapor phase corrosion inhibition of metals, particularly iron, steel and other ferrous metals, and articles made therefrom, and is especially concerned with the production of new and highly useful transparent heat-scalable sheets carrying or embodying therein vapor phase corrosion inhibitors the vapors of which are gradually released, in use, to effect the inhibition of the corrosion of the metals or metal articles which are wrapped or otherwise enclosed in said sheets.

In U.S. Patent No. 2,829,080, transparent heat-scalable sheets are disclosed comprising a transparent organic iilm base essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent organic covering iilm bonded to the film base and pervious to the passage therethrough of the corrosion inhibiting vapors, and a vapor phase corrosion inhibitor compatible with and embodied in said cover iilm.

The transparent heat-sealable vapor phase corrosioninhibitor carrying sheets of the aforesaid U.S. patent constitute a marked improvement over sheet materials for such purposes previously known in the art, as is fully brought out in the said patent. It has, nevertheless, been found, in accordance with the present invention, that significant improvements result if, in place of the vapor phase corrosion inhibitors disclosed in said patent, certain particular materials, described below in detail, are utilized. Furthermore, it has been found, pursuant to the present invention, and as will also be set forth below, that additional improvements result by reason of the employment of particular organic film base and cover iilm materials, and in particular details of the arrangement of said materials.

In accordance with the present invention, Ias in th aforesaid patent, the transparent heat-scalable sheets comprise a transparent organic film base, which may or may not be la polymer but which is essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent organic covering film which is bonded to said transparent organic film base and which is pervious to the passage therethrough of said corro-sion inhibitor vapors, and a vapor phase corrosion inhibitor compatible with and embodied in or adjacent to said organic covering film or, in other words7 in operative relation to said lms.

Despite their excellent functioning in general, various of the vapor phase corrosion inhibitors disclosed in said patent, for example, the organic nitrites -and inorganic nitrites, when embodied in the transparent films, cause a slight discoloration or yellowing of said sheets upon the passage of time, for instance, a few weeks, and which, under certain circumstances, may be regarded as somewhat objectionable even though the corrosion inhibiting properties of said sheets are in no way impaired. We have discovered, however, and among other things, that if the vapor phase corrosion inhibitor utilized is a straight chain C6 to C10 alkanoic acid, or a C7 to C11 aromatic monocarboxylic acid, or mixtures of one or more of said alkanoic and said aromatic monocarboxylic acids, the clarity of the sheets is not impaired and discoloration does not take place even after very prolonged periods of time. The C6 to C10 alkanoic acids comprise caproic, enanthic, caprylic, pelargonic and capric acids. Typical 3,080,211 Patented Mar. 5, 1963 ICC of the aromatic monocarboxylic acids 'are benzoic, toluic and tertiary butyl benzoic acid. These acids should, of course, be used in such proportions in or adjacent to the cover film as not unduly to impair the desired transparency or clarity of the finished sheet. Generally speaking not more than about 5% by Weight of any one of said acidsV can be incorporated into the cover film Without causing or tending to cause a slight haze. We have found, however, that mixtures of said acids in many cases can be used in substantially greater proportions Without causing haze. Thus, for instance, using equal Weights of Abenzoic acid and pelargonic acid as the vapor phase co1'- rosion inhibitor, as much as about 20% by weight can be incorporated into the cover film without impairing the clarity of said lilm or of the finished sheet. In general, where mixtures of Ibenzoic acid with one or more of the aforesaid alkanoic acids notably pelargonic acid, are utilized, a good working range is from l to 3 parts of benzoic yacid with from 3 to l parts of pelargonic acid or others of said alkanoic acids or mixtures of said alkanoic acids, said parts being by weight, and particularly preferred are approximately equal parts by weight of the benzoic and alkanoic acid or acids.

The transparent organic lm bases and transparent covering films may be selected from those which have been disclosed in the aforesaid patent and the techniques of producing the final transparent heat-scalable sheets containing the vapor phase corrosion inhibitors disclosed above in this specification may be those which are de scribed in said patent, the pertinent portions of said patent being incorporated herein by reference.

We have found, however, that exceptionally satisfactory results are obtained by using an ethylene glycol terephthalic acid polymer (Mylar) as the -base film in conjunction with a top coating or covering film of transparent cellulose acetate butyrate and an intermediate layer of a transparent adhesive, notably, an acrylonitrile butadiene copolymer. The base film in this particular embodiment is desirably 0.5 to 1.5 mil thickness; the top coating or film is advantageously about 0.3 to 0.4 mil thickness; and the intermediate layer, which is of adhesive character, is

about 0.6 to 0.7 mil thickness. While all of the aforesaid volatile corrosion inhibitor could be incorporated into the covering film, it has been found to be especially advantageous to include a portion, yand especially the major portion, of said corrosion inhibitor in the intermediate layer of transparent adhesive where this technique of making the finished sheets is utilized. This results in effectively meeting the problem of blocking or cracking. Thus for example, where a polyacrylate transparent resin is used as Vthe top or covering film, it not infrequently tends to crack when the finished sheet is bent. If a softer covY ering film is used as, for instance, by adding plasticizers, the cracking problem is eliminated but then blocking is encountered when the finished film is made into a bag. The inclusion of the alkanoic acids or the aromatic monocarboxylic acids, or mixtures of said acids, `aids markedlyl the present invention, other transparent materials which are particularly satisfactory for use as base films are the polycarbonates such as those sold under the designation Lexan (General Electric Company), and the polyester Tire & Rubber Company). All of these may be classed as polyesters, the polycarbonates constituting a special class of polyesters. Suitable polycarbonate ilms are, in general, esters of aromatic glycols or bisphenols with carbonio acid, illustrative of which are reaction products of bisphenol A and phosgene, or reaction products of bisphenol A and dimethyl carbonate. Other suitable polyester films comprise, generally, esters of dibasic aromatic acids with glycols. The polycarbonates and the polyesters and methods for their production are, per se, known in` the art. The films utilized in accordance with our present invention should most desirably be flexible.

' It is especially advantageous to utilize a transparent adhesive intermediate the transparent base iilm and the transparent covering film. Such transparent adhesives are most desirably rubbery materials. Particularly satisfactory results have been obtained with copolymers of acrylonitrile and butadiene, a typical example of which is the product sold under the designation Chemigum N-6B (Goodyear Tire & Rubber Company) which contains approximately 32% by weight of acrylonitrile. Other typical suitable transparent adhesives are robbery acrylonitrile-butadiene copolymers sold under such designations as Hycar 1512, Hycar 1552, Hycar 1561, Hycar 1577 (B. F. Goodrich Chemical Co.); Chemigum 235, Chernigum 245 (Goodyear Tire & Rubber Company); Butaprene NSP 169' (Firestone Tire and Rubber Company), and the like. These substances are per se known in the art. It is preferred to utilize such commercial products as contain antioxidants but, if desired, any suitable antioxidant can be incorporated there- 1n.

The thickness of the transparent heat-scalable sheets inhibitor is utilized in an amount sufficient to constitute, by Weight, from about 0.1 to `about 1 or 2 grams per square foot of the area of the transparent sheet. Preferably, the amount of Vapor phase corrosion inhibitor used will, in most cases, range from about 0.2 to about 0.6 gram per square foot of area of the sheet. In terms of the amount, by Weight, of the vapor phase corrosion inhibitor based on the weight of the transparent organic cover film, good results are obtained, in at least most cases, with the vapor phase inhibitor comprising from about 5 to about 20%, by weight, of the cover lm.

The following table illustrates speciiic examples of transparent heat-scalable sheets made in accordance with the present invention. It will be understood that these examples are given merely by way of illustration and are not intended in any way to be limitative of the full scope of the invention.

The aforesaid coatings, as indicated above, can be applied to the base lm, for instance, the ethylene glycolterephthalic acid polymer iilm, in any suitable manner and through various existing types of coating equipment. The accompanying drawing shows, in schematic form, an -arrangement of equipment which has been found to be very satisfactory, particularly from the standpoint of economy -in that the intermediate adhesive and the top or cover lilrn are applied on one side of the base lilm in a single pass ofthe said base lrn.

ln the accompanying drawing, numeral l indicates a drying oven through which air, preferably previously heated air, from conduit 2 is passed, advantageously Suthciently rapidly so as to avoid the formation of air-organic solvent concentrations within the explosive range Where certain organic solvents are involved. It is preferred that the drying oven house a bank or banks of infra red heatof the present invention is, of course, variable. In all ers in order to reduce or eliminate the tendency of sur- Table Exam le Base Film Im ermeable Intermediate Vapor Phase Corrosion Inhibitor and No.p to V(apo1r)s) Cover Film Adhesive Percentage by Weight Thereof Based Layer on Cover Film 1 Ethylene glycol-terephthalic Cellulose Acetate lilutyrate.`-` Pelargonic acid (5%).

acid polymer (Mylar). h 2 dn dn Chemigurn Equal parts of pelargonlc acid and N-GB. benzoic acid (15%) equally distribged in adhesive layer and in cover 3 rln rln --.do Equal parts oi pelargonlc acid and benzoic acid (15.4%) 75% of which is distributed in adhesive layer and 25% in cover iilm.

4 dn Vinyl chloride-vinyl acetate Equal parts oi pelargonic acid and cvoxpilmer (Vinylite benzoic acid (12%). H dn Polyethylacrylate (Rhoplex 1 part pelargonic acid and 2 parts WN-80). benzoic acid (10%).

NOTE.-Deposit of the cover lm in each of the above examples is from organic solvent solutions, specifically, acetone Solutions oi the cellulose acetate butyrate, and of the Chernigum where used, on the base lrn.

instances, however, they should not be so thick as to interfere with their ilexibility and the ability to utilize the same for Wrapping and packaging purposes. In general, the finished transparent sheet desirably has a thickness-of about 0.5 to about 5 to l0 mils, particularly, from about 1 to 5 mils. The transparent organic lm base, for example, may have a thickness of the order of 0.5 to 1.5 mil and the thickness of the transparent organic covering film may, for instance, also be of the order of 0.3 to 0.5 mil but may be of a thickness of 1 to 3 or 5 Vmils so that the total thickness may be, for instance, from 1 to 5 mils for the iinal iinished transparent sheet.

The amount of the vapor phase corrosion inhibitor which is embodied in the transparent organic covering film or, in other words, directly into or adjacent said latter `film or in operative relation to said lm, is somewhat variable, depending, among other things, upon the desired useful life of the sheet from the standpoint of its etectiveness to inhibit the corrosion of metals wrapped therein. Generally speaking, the vapor phase corrosion face crusting and entrapment of organic solvent. A lilm or sheet 3, most desirably continuous, of the ethylene glycol-terephthalic acid polymer is fed from a roll 4 thereof beneath a tensioning roller 6 over a coating roller 7 disposed over a trough 8 carrying an organic solvent solution of the transparent adhesive material and, desirably, atleast a part of the alkanoic acid and/ or aromatic monocarboxylic acid. The underside of the film or sheet 3 Vpicks up an excess coating from the roller 6 of the said solution. The thus excess coated lm or sheet passes into contact with a wire bar 9, namely, a metal bar Wrapped with wire. The .said organic solvent solution passes through the crevices in the wire bar and then flows to form a smooth coating on the sheet or lm, excess organic solvent solution draining back into the trough S. The coated iilm or sheet then passes into the drying oven which, in the illustrative example of organic solvent solution of the adhesive material, may be maintained at about 200 degrees -F. The organic solvent is essentially evaporated and the ilm or sheet then passes to a device for applying the top or cover film, for instance, cellulose acetate butyrate. Since the dried first coating applied to the ethylene glycol-terephthalic acid film or sheet may be somewhat tacky, the top or cover coating or film should be applied before the finished film or sheet is wound into a roll. After the tacky rubbery coating solution is applied and dried, the said base coated film is passed out of the drying oven and over a roller 11 disposed over a trough 12. It Will be noted that the adhesive layer is now uppermost. An organic solvent solution of the cover coating material containing the added alkanoic acid and/or aromatic monocarboxylic acid is then discharged through a sluice 13 into the dried tacky surface and the quantity and even distribution thereof is controlled by a wire bar 14, excess solution dropping into the trough 12. The film or sheet then passes back into drying oven 1 to effect removal of the organic solvent and then passes out of said oven and is cooled by air over a chill roll 16, then over rollers 17 and finally to windup roller 18 where the finished film or sheet is wound into rolls. The equipment should be operated to avoid condensation of atmospheric moisture on the applied coatings before the film or sheet enters the drying oven so as to avoid haziness in the finished films or sheets. This can readily be accomplished by controlling the rate of movement of the film or sheet, the relative humidity, temperature and solvent volatility through the selection of proper solvents.

In an illustrative example, a solution of Chemigum N-6B in acetone is very suitable as the solution from which the adhesive layer is laid down. The Chemigum N-6B is first advantageously Worked on a rubber mill for a few minutes and then cut into small pieces to facilitate its solution in the acetone. For the cover coating, a typical illustrative coating solution is a 30% solution in acetone of a transparent cellulose acetate butyrate.

What is claimed as new and desired to be protected by Letters Patent of the United States is:

l. A transparent heat-scalable sheet comprising a transparent organic film base essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent organic covering film bonded to said film base and pervious to the passage therethrough of said corrosion inhibiting vapors, and, as a vapor phase corrosion inhibitor compatible with and in operative relation to said cover film, at least one member of the class of C6 to C10 alkanoic acids.

2. A sheet in accordance with claim l, wherein said transparent organic film base is an ethylene glycol-terephthalic acid polymer, and the covering film is cellulose acetate butyrate.

3. A transparent heat-sealable sheet comprising a transparent organic film base essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent organic covering film bonded to said film base and pervious to the passage therethrough of said corrosion inhibiting vapors, said sheet having a thickness of about 0.5 to 5 mils, and, as a vapor phase corrosion inhibitor compatible With and in operative relation to said cover film, up to 20%, by weight of said covering film, of at least one member of the class of C6 to C10 alkanoic acids.

4. A transparent heat-sealable sheet comprising a transparent organic film base essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent organic covering film bonded to said film base and pervious to -the passage therethrough of said corrosion inhibiting vapors, said sheet having a thickness of about 0.5 to 5 mils, and, as a vapor phase corrosion inhibitor embodied in said covering film in a total amount of from about 5 to 20% by weight of said covering film, a mixture of benzoic acid and at least one member selected from the group consisting of C6 to C10 alkanoic acids.

5. A sheet in accordance with claim 4, wherein said transparent organic film base is an ethylene glycol-terephthalic acid polymer, and the covering film is cellulose acetate butyrate.

6. A transparent heat-sealable sheet comprising a transparent organic film base resistant to the passage therethrough of corrosion inhibiting vapors, a transparent organic covering film` bonded to said film base and pervious to the passage therethrough of said corrosion inhibiting vapors, said sheet having a thickness of about 0.5 to 5 mils, and, as a vapor phase corrosion inhibitor in operative relation to said covering film in a total amount of from about 5 to 20% by weight of said covering film, a mixture of approximately equal parts of benzoic acid and pelargonic acid.

7. A transparent heat-scalable sheet comprising a transparent ethylene glycol-terephthalic acid polymer film base essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent organic covering film bonded to said film base through a layer of a transparent adhesive and pervious to the passage therethrough of said corrosion inhibiting vapors, and a vapor phase corrosion inhibitor in operative relation to said covering film and being present in a total amount of from about 5 to 20% by weight of said covering film, said vapor phase corrosion inhibitor being selected from the class consisting of at least one member of the C6 to C10 alkanoic acids. i

8. A transparent heat-scalable sheet comprising a transparent ethylene glycol-terephthalc acid polymer film base essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent covering film bpnded to said film base through a transparent adhesive and pervious to the passage therethrough of said corrosion inhibiting vapors, and, as 'a vapor phase corrosion inhibitor embodied in said covering film in a total amount of from about 5 to 20% by Weight of said covering film, a mixture of approximately from 1 to 3 parts of benzoic acid with from 3 to 1 parts of pelargonic acid.

9. A transparent heat-scalable sheet comprising a transparent polyester film base essentially resistant to the passage therethrough of corrosion inhibiting vapors, a transparent coating on said film base which coacting comprises an acrylonitrile-butadiene copolymer, and a transparent cellulose acetate butyrate covering film embodying therein at least one member selected from `the class consisting of C6 to C10 alkanoic acids.

10. A transparent heat-scalable sheet comprising a transparent ethylene glycol-terephthalic acid polymer film base, a transparent coating on said film base which coating comprises an acrylonitrile-butadiene copolymer, and a transparent cellulose acetate butyrate covering film embodying therein a small percentage by weight of each of benzoic acid and pelargonic acid.

11. A transparent heat-sealable sheet comprising a transparent ethylene glycol-terephthalic acid polymer film Ibase, a transparent coating on said film rbase which coating comprises an acrylonitrile-butadiene copolymer embodying from about 5 to 6% by weight of each of benzoic acid and pelargonic acid, and a transparent cellulose acetate butyrate covering film embodying therein a small percentage by weight of each of benzoic acid and pelargonc acid.

l2. A transparent heat-scalable sheet comprising a transparent ethylene glycol-terephthalic acid polymer film base, a transparent coating on said film base which coating comprises an acrylonitrile-butadiene copolymer embodying from about 5 to 6% by weight of each of benzoic acid and at least one member of the group of C6 to C10 alkanoic acids, and a transparent cellulose acetate butyrate covering lm embodying therein from 1 to 3% by weight of each of benzoic acid and at least one member of the group of C6 to C10 alkanoic acids.

K (References on following page) 7' 8 References Cited inthe le ofths patent 2,707,551. Shnitzler` May 3, 1955. 2,775,574. SIOc-:Ombeet al. Dec. 25, 1956 UNITED STATES PATENTS" w 2,829,080, Eessler e181 Apr. 1,1958 631089 Anderson APP-'18481953 2,848,298 ROSS eral. Aug. 19,1958 996691507 Young' --Feb- 16s 1954 5 2,986,447 Raifsnider May 3o, 1961 2,673,191' Wolf Mr. 23, 1954-'Y 

1. A TRANSPARENT HEAT-SEALABLE SHEET COMPRISNG A TRANSPARENT ORGANIC FILM BASE ESSENTIALLY RESISTANT TO THE PASSAGE THERETHROUGH OF CORROSION INHIBITING VAPORS, A TRANSPARENT ORGANIC COVERING THE FILM BONDED TO SAID FILM BASE AND PERVIOUS TO THE PASSAGE THERETHROUGH OF SAID CORROSION INHIBITING VAPORS, AND, AS A VAPOR PHASE CORROSION INHIBITOR COMPATIABLE WITH AND IN OPERATIVE RELATION TO SAID COVER FILM, AT LEAST ONE MEMBER OF THE CLASS OF C6 TO C10 ALKANOIC ACIDS. 